A thread-delivery device is known from German AS No. 1,585,298. It has, as a thread-control element, two levers which are connected through a common axle approximately in a U-shape and are supported swingably by means of same in planes which are parallel with respect to the axis of the thread-guiding roller. The levers extend on both sides of the thread-guiding roller and each carries at its end an eyelet for the thread. A spring engages the common axle. It is initially tensioned such that it holds or urges the levers in a rest position in which the thread which is guided through the two eyelets rests on an area of the thread-guiding roller which is free from the delivery belt. This position is possible if the thread is not exposed to any tension. If the thread is delivered or consumed by the textile machine, the tension of the delivered thread is sufficient to swivel the levers against the force of the spring so that the thread runs in the area of the thread-guiding roller on which also runs the delivery belt, which thereby conveys the thread. If less thread is consumed, then the withdrawal tension of the thread becomes less, the levers move upwardly and the thread delivery is interrupted. At the same time trip cams which are arranged on the lever axis switch on a signal lamp and/or switch off the machine drive. The time period needed in order for the spring to pull the thread out from between the delivery belt and thread-guiding roller, such as during a tension drop, is too great for some purposes. This is true, for example, when working on a stripe machine, which produces color-striped goods and therefore often changes between different threads at every thread processing location. This change must occur quickly and exactly, and the thread which is not in operation, which is separated and clamped at the processing location, should not continue to be delivered. It is not possible to increase the force of the spring in order to speed up the lever movement, since the spring force and the tension of the delivered thread must be adjusted directly to one another for the correct function during the delivery, and the thread tension is supposed to be maintained as low as possible.
The purpose of the invention is to construct a device of the described type with simple means so that the thread delivery, upon a dropping in the tension of the delivered thread, is interrupted within the shortest period of time.
The inventive device accelerates the interruption of the thread delivery substantially through the cooperation of several factors: The tension feeler, forcedly disposed in the path between the thread-control element and the processing location, experiences a tension change before the tension change reaches the thread-control element itself. Its reaction movement does not move the thread itself proportionally to said movement, but results in a naturally very quick electric switching operation, to which an electromagnet reacts. Its mechanical coupling with the thread-control element can, since it does not have any influence on the delivery tension of the thread, work with any desired force input or any suitable movement ratio, so that the thread-control element can instantaneously move the thread out of the area of the delivery belt. A further advantage of the device consists in the tension feeler changing, during its movement, the thread path of the unwinding thread. The small amount of thread which is subsequently delivered, in spite of the quick interruption, is absorbed by this detour or changing of the thread path.
For a device of the above-described type, with a swingably supported thread-control element which is loaded by a spring in a direction toward the position which guides the thread over the delivery-belt-free area, the spring can advantageously be engaged at the free end of a magnetic arm, which arm is connected to the thread-control element in the area of its swivel axis, and the electromagnet can be arranged adjacent to the arm so that it swivels same, when switched on, against the spring force.
In this embodiment, the unwinding thread on the one hand and the spring on the other hand are still in direct mechanical connection with the thread-control element. The direct reciprocal force effect is, however, interrupted by the electromagnet, which acts in dependency from the thread tension against the spring. The spring force in this manner does not at all effect the spring tension, which through this can be kept low in the desired manner. The spring can, however, be designed stronger than is possible in a direct connection. During release from the electromagnet, the spring correspondingly quickly swivels the thread-control element and ends the thread delivery. Just as quickly the electromagnet takes care of the swivelling of the thread-control element into the delivery area, when the thread is again grabbed and tensioned at the processing location. The thread tension must not first build up which is capable of overcoming the spring tension.
In an advantageously simple manner it is possible for the tension feeler to have two lever arms with one thread eyelet for the delivered thread at the free end of the first lever arm and a contact piece at the end of the second lever arm, which feeler can be spring-loaded swingably supported such that the contact piece, during delivery of the thread, closes the circuit of the electromagnet and opens same during a drop in the tension. A minimum swivelling path is needed for the opening and closing of the contact. It can additionally be influenced by the length relationship of the two lever arms, so that the spring which engages the tension feeler can be very weak and has no significant influence on the thread tension.
An advantageous arrangement of the tension feeler in the thread path is achieved in a simple manner by positioning the thread eyelet of the tension feeler within the path of the delivered thread, and having positioned before it a first stationary guide eyelet and positioned after it a second stationary guide eyelet, such that in the case of normal delivery tension the thread eyelet lies between the two guide eyelets but moves out from between the guide eyelets during a drop in the tension, thereby forming a thread loop out of the subsequently delivered thread.
The tension feeler can advantageously take over a further function as a thread-breakage monitor, in that it in the case of a thread breakage can be moved, by the return spring which loads it against the thread tension, into a switching-off position in which the contact piece closes a cut-off circuit for the textile machine.
Further details and advantages of the invention can be taken from the description of an exemplary embodiment, which is illustrated in the single FIGURE of the drawing.